Karl Peter Heinzen was a revolutionary author who resided mainly in Germany and the United States. He was one of the German Forty-Eighters. He advocated terrorist violence against ruling dynasties and uninvolved civilian populations as a means to an end.

Karl Hermann Bitter was a Prussian statesman and writer on music.

Karl Hess was an American speechwriter and author. He was also a political philosopher, editor, welder, motorcycle racer, tax resister, and libertarian activist. His career included stints on the Republican right and the New Left before embracing a mix of left-libertarianism and laissez-faire anarcho-capitalism. Later in life, he summed up his role in the economy by remarking "I am by occupation a free marketer ."

Karl Hillebrand (17 September 1829 - 19 October 1884) was a German author.

Karl Friedrich Christian Hoeck was a German classical historian and philologist as well as a librarian.

Karl Holl was a professor of theology and church history at Tübingen and Berlin and is considered one of the most influential church historians of his era.

Karl Hopf or Carl Hermann Friedrich Johann Hopf was a historian and an expert in Medieval Greece, both Byzantine and Frankish.

Karl Immanuel Nitzsch was a German Lutheran church leader. He was the father of theologian Friedrich August Nitzsch.

Karl Leberecht Immermann was a German dramatist, novelist and a poet.

Karl Isidor Beck was a Hungarian-Austrian poet.